1. Field of the Invention
The present invention relates generally to a mold for producing, or molding, a disc and, more particularly, to an apparatus for improving the releasability of the disc from the mold.
2. Description of Related Art
Injection molding apparatus for molding a disc has hitherto been performed in such a manner as shown in FIG. 2. A synthetic resin material is injected through a sprue bushing 4 into a cavity 3 defined by a mirror surface 14 of a stationary mold half 1 and a stamper 13 set on a mirror surface 10 of a movable mold half 2 and is molded as a disc 30.
Further, the releasing of the molded disc 30 from the mirror surface 14 and the stamper 13 has been performed by blowing air from a stationary-side air hole A toward the stationary mold half 1 side of the disc 30 and, at the same time, additional air is blown from a movable-side air hole B toward the movable mold half 2 side of the disc 30. Thus, the disc 30 is released respectively from the stamper 13 and the mirror surface 14 of the stationary mold half 1. Thereafter, an ejection bar 7 is moved by ejector pins 9 to eject and release the disc 30.
Although no influence is exerted on the disc 30 at the time of releasing the disc 30 from the mirror surface 14 of the stationary mold half 1 by blowing air from the stationary-side air hole A, when the disc 30 is released from the stamper 13, by the blowing air from the movable-side air hole B, signal pits on the surface of the stamper 13 offer resistance to the air-blow. Thus, in the course of the disc 30 being released from inside to outside (center hole to outer edge), that is, before the air blown from the movable-side air hole B completely reaches around the outermost periphery of the disc, the ejection bar 7 starts to operate.
As a consequence, a boundary line of the air that defines reached and unreached portions between the disc 30 and the stamper 13 appears on the disc. This often results in the appearance of stains on the disc.